Read the passage carefully and answer the questions :

The speed at which a chemical reaction takes place is called the rate of reaction. The rate of reaction depends on various factors like concentration of the reactants, temperature, etc. The relation between the rate of reaction and the concentration of reacting species is represented by the equation r = k[A]x[B]Y, where x and y are the order of the reaction with respect to the reactants A and B, respectively.

The overall order of the reaction is x ++ y. The rate of reaction can also be increased by the use of a catalyst which provides an alternate pathway of lower activation energy. It increases the rate of forward and backward reaction to an equal extent. It does not alter the Gibbs energy of the reaction.

Q) The role of a catalyst is to change

The correct option is: Activation energy of a reaction.

Explanation:

A catalyst is a chemical substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself. According to the provided passage, the rate of a reaction can be increased by using a catalyst because it provides an alternate pathway for the reaction. This alternate pathway has a lower activation energy compared to the uncatalyzed pathway.

By lowering the activation energy barrier, more reactant molecules possess the minimum energy required to cross the transition state and transform into products per unit of time. The passage also explicitly states that a catalyst "does not alter the Gibbs energy of the reaction." Similarly, a catalyst does not alter the overall enthalpy of the reaction or the equilibrium constant, as it accelerates both the forward and backward reactions to an equal extent. Therefore, the primary role of a catalyst is to change the activation energy of a reaction.